Tip-off oven



Aug. 6, 1963 F. R. JOHNSON TIP-OFF OVEN 2 Sheets-Sheet 1 Filed Oct. 24,1960 FlG.2.

lNVENTOR N o S N Y H E o N Iv R R o C T R E s D I. E R F Aug. 6, 1963 F.R. JOHNSON 3,100,251

TIP-OFF OVEN FiledOct. 24, 1960 2 Sheets-Sheet 2 INVENTOR: FREDERIC R.JOHNSON,

3,160,251 TlP-GFF (ll/EN Frederick. Johnson, Chittenango, N.Y.,assignorto General Electric Company, a corporation of New York FiledOct. 24, 1960, Ser; No. 64,55h Claims. (Cl. 21919) The present inventionrelates to the manufacture of electronic tubes such as cathode raytubes, and more particularly to an improved electrically heated tip-offoven for sealing closed the exhaust tubulation of a cathode ray tube orthe like.

In the manufacture of eletcronic tubes such as cathode ray tubes it isconventional to exhaust the envelope of the tube through a pipe ortubulation which extends integrally from the envelope, usually from thecenter of the end Wall-or stem which closes the distal end of the tubeneck. The tubulation may be made of glass or other suitable heatsoften'able and scalable material. After the tube has been exhausted toan appropriate degree, the tabulation is sealed at a point close to theenvelope wall by locally heating it tosufficient softness so that alocalized portion of the wall of the tabulation collapses underatmospheric pressure and fuses to form a closed gas-tight seal forthetube envelope, after which the remainder of the tabulation is removed.

Electrically fired ovens for the purpose of producing the desiredlocalized heating of the tubulation have been used in the past. Howeverthe ovens used heretofore have had numerous disadvantages particularlyas respects the time, efiort and. expense involved in maintaining themin satisfactory operating condition for desirably long periods of time.The importance of the repair-ability and maintainability of tip-offovens will be better appreciated if it is understood that one such ovenis attached to each tube undergoing exhaust, and since it is customaryfor an exhaust cycle to have a substantial duration, for example aboutone hour in thecase of television picturetubes of popular size, afactory capable of producing several hundred tubes per hour wouldrequire atv least that number of tip-oft ovens in use at any one time.Also, since each tube has its own individual oven temporarily affixedthere to during the exhaust cycle, such ovens are often employed, attimes other than during the actual exhaust cycle, as convenientelectrical sockets through which desired potentials may be applied tocertain of the electrodes of the tube for such purposes as activatingthe cathode or testing the condition of the tube. As a consequence itwill be appreciated that in a manufacturing plant having even a moderateexhaust capacity, a substantial number of such tip-off ovens is requiredto be continuously in operation.

"Moreover, the environmental extremes to which such ovens are subjectedfurther underscore the importance of easy repairability andmaintainability. The high temperatures and frequent temperature changesof the exhaust cycle to.which the tip-01f ovens are subjected, and thehigh temperatures repeatedly generated within the tip-off ovensthemselves as necessary to soften the tubulation sufficiently to seal itclosed, have heretofore made necessary frequent replacement of ovenswith cracked or distorted parts. Also, the tendency for. moltentubulation material, particularly when the tubulation is glass, tocollect on the heating elements or other part of the ovens and build upa deposit which is difiicult and time consuming to remove, and which mayeither'impair the heating efiiciency of the oven or clog the interior ofthe oven such that the tubulation of a tube will not fitinto the oven,has heretofore made frequent replacement necessary.

A principal object of the present invention is to provide anelectrically fired tip-off oven having a lengthened service life incomparison with ovens of the prior art.

BJMLZSI Patented Aug. 6, 1963 Another object is to provide an oven inwhich the heating element per se is readily removable and replaceable,quickly and inexpensively.

Another object is to provide a tip-off oven whose first cost isrelatively small in comparison with ovens of the prior art.

Another object is to provide a tip-off oven which can be readilydisassembled, either completely if required, or to the partial extentnecessary for performing those repairs most frequently required.

Another object is to provide a tip-off oven which is particularlysuitable for accommodating a wide variety of tabulation sizes and stemlead circle sizes. H

These and other objects of the invention will be apparent from thefollowing description taken in conjunction with the accompanyingdrawings, wherein:

FIGURE 1 shows a cathode ray tube mounted on an exhaust cart or buggysuitable for being conveyed through an exhaust oven and titted with anelectrically fired tipoff oven constructed in accordance with thepresent invention;

FIG. 2 is an enlarged partially sectionalized view of a portion of thestructure of FIG. 1;

FIG. 3 is an exploded perspective view, to ajdiminished scale, of thetip-elf oven shown in FIG. 2;

FIG. 4 is an exploded perspective view of certain of the elements shownin -FIG. 3.

Turning now to FIGS. 1 and 2 of the drawing, a portable cart or buggy 2is shown arranged to carry a, cathode ray tube 4 in a support bracket 6,and provided with suitable exhaust pumping means. Sconnected by a hose10 to the tubulation- 12 extending integrally downward from the stem 14-at the end of the neck 16 of the tube. A tip off oven '18 constructedaccording to'the present invention'is fitted on the tube in surroundingrelation with the tabulation adjacent the stem.

The tip-oil? oven shown includes a one piecegenerally cylindrical body20 of insulating material, which is preferably a ceramic member suitablefor Withstanding'the thermal shock and high temperatures involved, andhaving an axial rth'roughbore 22 forming a chamber, 2 4 foraccommodating the tubul-ationlZ of the tube to be .exhausted.

Closing the upper end of the throughbore22 isafstilf top plate 26, shownas of sandwich construction, and as better shown in FIG. 3 consisting ofa central stiff layer 28, which may be metallic, between heat andelectrically. insulating layers 50 and 52, which may be made for exampleof matted mica. A stitf'bottom plate '54 of suitable insulating materialsuch as asbestos fibre board closes the lower end of the throughbore.The topplate 26 and bottom plate 54 are secured to the body' by bolts 56which extend through the plates and through axial passages in the body,and are retained by nuts: 58 on their lower ends. Both the top plate andbottom'plate are centrally apertured to accommodate the tubulation 12,and the top plate is also provided with additional openings 60 throughwhich the electrode lead wire 62 extending from the envelope wall of thetube, in this case from the tube stem 14, may extend into electricalconducting engagement with suitable electrical contacts 64 of thetipoffoven. If contact of the stem leads 62 with the'top plate would result inshort circuiting the stem leads, openings '60 should preferably be ofsufficient size to avoid such short circuiting contact.

The throughbore 22 is enlarged at its upper end by a plurality ofangularly spaced radially extending grooves 66, each positioned oppositeone of the stem lead openings 6i) in the top plate. The outer ends ofgrooves 66 are connected through radially extending passages 67 to theexterior cylindrical surface of'the body. Disposed within the groovesare resilient forked electrical contacts 64 clamped in place by threadedelectrically conductive studs 68 extending through the passages andsecured by nuts 70 on their outer ends. Certain of the studs 68 and nuts70 serve respectively as electrically conductive leads and externalterminals for the contacts 64.

The lower portion of the throughbore 22 is enlarged to form acylindrical chamber 24 provided at its upper end with an axially facingradially extending annular shoulder 72. Situated within the chamber 24is a heating element support 74 of insulative material, preferablyceramic. The support 74 is relatively small and light in weight incomparison with the body, and consists of an annular sleeve formed of aplurality of parti-annular, here shown as parti-cylindrioal, segments76. Within the support is a heating element 78 consisting of anelectrical conductor of annular shape, here shown as a cylindricalspiral, and which may be made of Nichrome or other suitable resistanceheating wire. The interior surfaces of the segments are provided with aplurality of spaced ridges or outstanding portions 80, shown as somewhatlike spiral threads. These outstanding portions 80 engage and providethe exclusive support for the heating element 78, as Well as holding theindividual increments or turns of the heating element in slightly spacednon-short-circuiting relation. One end of the heating element is broughtout through a radial groove 82 in the lower face of the body, and theother end is brought out through an axially extending groove 84 in thechamber and a radial groove 86 in the lower face of the body. Theterminal ends of the heating element are secured to appropriate ones ofthe studs 68 by nuts 7 0, these studs and nuts thus serving as externalterminals for the heating element.

The heating element 78 and heating element support 74 are retainedwithin the chamber merely by the bottom plate 54, and the heatingelement support 74 is dimensioned to have a loose enough fit within thechamber 24 to facilitate slight radial movement of the segments such asto accommodate expansion of the heating element, while insuringcontinuous proper support and separation of the individual turns of theheating element by outstanding portions 80 during oven operation. Thissegmentation and loose fit of support 74 further facilitates removal ofthe heating element 78 and heating element support 74 as may be desiredwithout disturbing the remainder of the oven.

An oven constructed as above-described has a number of advantages.'First the segmented sleeve-like heating element support 74, dimensionedto accommodate expansion of the heating element 78 during oven operationwithout cracking of itself or the oven body 20', and providingcontinuous support exclusively of insulating material for each turn ofthe heating element in separated non-short-circuiting relation with itsneighbor, completely avoids the major causes of oven failure, namelyinsulator breakage and heating element short circuiting or burn out.This provides a substantial increase in oven life. Next all that isrequired to remove the heating element 78 or heating element support 74from the oven, for replacement or repair, is to remove the bottom plateand loosen the two nuts 70 holding the ends of element 78, after whichthe heating element support 74 and heating element 78 readily drop outof the chamber 24. No other parts of the oven need be disassembled topermit removal of the heating element or heating element support. Thusthe heating element and heating element support, which are the partsmost subjected to impairment by fouling with molten glass or othermaterial, and which are most subject to failure mechanically orelectrically during operation of the oven, may be readily replaced.

Moreover, the fact that the heating element itself may be readilyseparated from the segments of the heating element support, and the factthat the heating element support 74 is small, light in weight and ofrelatively easily moldable shape, means that any of these individualparts may be readily discarded and replaced as individual items at verymodest cost without requiring replacement of any other parts of theoven. Additionally, the one piece ceramic body Ztl, serving as thecontainer for both the heating element 78 and stem lead contacts 64,minimizes first cost of the oven and simplifies assembly and disassembly. Further the partial radial grooves 66 enables con tacts 64 to beclamped in place by studs 68 without the expense of providing anythreaded holes in body 20.

It will also be evident that since the heating element is of largerdiameter than that of the stem lead circle or pin circle defined by thestern leads of the tube, tubes having pin circles of different diametersmay be readily accommodated in the oven by merely changing the spacingof the openings in the top plate. And thus it will be evident that theoven is readily adaptable for use with a variety of tube types havingdifferent pin circle diameters.

It will be appreciated by those skilled in the art that the inventionmay be carried out in various ways and may talce various forms andembodiments other than those illustrative embodiments heretoforedescribed. It is to be understood that the scope of the invention is notlimited by the details of the foregoing description, but will be definedin the following claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. An electronic tube tubulation tip-off oven comprising a body having acentral chamber through which the exhaust tubulation of a tube isadapted to extend, a heating element of annular coil form situatedwithin said chamber and dimensioned to surround an exhaust tubulationextending therethrough, a removable and replaceable heating elementsupport situated between the heating element and the wall of saidchamber, said support having on the interior surface thereof a pluralityof electrically insulative outstanding portions respectively engagingand continuously supporting in non-shor-t-circuiting relationshiprespective successive increments of said heating element, and retainingmeans at least partially closing the botto of said chamber forreleasably securing said heating element support in said chamber topermit said support, upon release, to fall freely from said chamber.

2. An electronic tube tubulation tip-off oven comprising a body having acentral chamber through which the exhaust tubulation of a tube isadapted to extend, a heating element of annular coil form situatedwithin said chamber and dimensioned to surround an exhaust tubulationextending theret-hrough, a removable and replaceable sleeve ofelectrically insulating material situated within said chamber insurrounding relation with said heating element, said sleeve having onthe interior surface thereof an outstanding portion of continuous coilconfiguration providing the exclusive support for said heating elementwithin said chamber to permit said support, upon release, to fall freelyfrom said chamber, and retaining means for releasably securing saidheating element support sleeve in said chamber.

3. In an electronic tube tubulation tip-ofi oven including a body havinga central chamber through which the exhaust tubulation of a tube isadapted to extend, and a heating element of annular coil form situatedwithin said chamber and dimensioned to surround an exhaust tubulationextending therethrough, a removable and replaceable heating elementsupport of electrically insulating material situated between the heatingelement and the wall of said chamber, said support being dimensioned toaccommodate heat expansion of said heating element during oven operationand having on the interior surface thereof a plurality of outstandingportions of continuous coil form respectively engaging and continuouslysupporting in non-short-circuiting relationship respective successiveincrements of said heating element, and retaining means at leastpartially closing the bottom of said chamber for releasably securingsaid heating element support in said chamber to'penmit said support,upon release, to fall freely from said chamber.

4. In an electronic tube'tubulation tip-off oven including a body havinga central chamber through which the exhaust tubulation of'a'tubeenvelope is adapted to extend, a heating element of annular coil formsituated within the central chamber and dimensioned to surround anexhaust tubulation extending therethrough, an annular heating elementsupport situated between the heating element and the wall of saidchamber, said support including a plurality of removable and replaceableparti-annular segments of insulating material dimensioned to accommodateheat expansion of said heating element during oven operation, each ofsaid segments having on the interior surface thereof a plurality ofoutstanding portions of coil form engaging and supporting in spacedrelationship from each other the respective turns of said heatingelement, and retaining means at least partially closing the bottom ofsaid chamber for releasably securing said segments in said chamber topermit said support, upon release, to fall freely from said chamber.

5. An electronic tube tubulation tip-off oven comprising an insulativebody having a central axially extending thnoughbore providing a chamberthrough which the exhaust tubulation of a tube envelope is adapted toextend, an axially facing shoulder at one end of said chamber, a heatingelement of cylindrical helical coil form situated within said chamberand dimensioned to surround an exhaust tubulation extendingtherethrough, a removable and replaceable cylindrical heating elementsupport situated between the heating element and the wall of saidchamber, said support including a plurality of parti-cylindricalsegments of insulating material, each of said segments having aplurality of spaced outstanding portions engaging and continuouslysupporting in spaced relationship from each other the respective turnsof said heating element, and releasable retaining means for securingsaid heating element support in said chamber.

6. An electronic tube tip-off oven comprising a body having a centralaxially extending throughbore providing a chamber through which theexhaust tubulation of -a tube envelope is adapted to extend, a coaxialannular axially facing shoulder within said chamber, a heating elementof cylindrical helical coil form situated within said chamber anddimensioned to surround an exhaust tubulation extending therethrough, aremovable :and replaceable heating element support of insulatingmaterial situated between the heating element and the wall of saidchamber, said support including a plurality of parti-cylindricalsegments, each of said segments having on the interior surface thereof aplurality of respective spaced ridges supporting and maintaining inspaced relationship from each other the respective turns of said heatingelement, external terminals on said body to which the ends of saidheating element are attached, a bottom plate removably secured to saidbody and covering the mouth of said chamber for holding said support insaid chamber and against said shoulder, and an apertured top platesecured to said body and covering the end of said throughbore remotefrom the mouth of said chamber.

7. An electronic tube tubulation tip-off oven comprising an annularceramic one piece body having a central chamber through which theexhaust tubulation of an electronic tube is adapted to extend, aplurality of grooves in one end face of said body each terminating atits outer end in spaced relation with the marginal edge of said endface, electrical contacts in said grooves for engaging the electrodeleads of a tube having its tubulation extending through said chamber,means for securing each of said contacts in its respective grooveincluding a stud extending through the portion of said body between theouter end of the respective groove and the exterior surface of saidbody, a heating element of annular coil for-m situated within thecentral chamber and dimensioned to surround an exhaust tubulationextending therethrough, a removable and replaceable heating elementsupport situated between the heating element and the wall of saidchamber, said heating element support having on the interior surfacethereof a plurality of outstanding insulative portions engaging andsupporting in spaced relationship from each other the respective turnsof said heating element, and re taining means for releasably securingsaid-heating element support in said chamber.

8. An electronic tube tubulation tip-01f oven comprising a one-pieceannular ceramic body having a central chamber through which the exhausttubulation of an electronic tube is adapted to extend, a plurality ofgrooves in one end race of said body extending radially from saidcentral chamber and terminating in spaced relation with the marginaledge of said end face, electrical contacts in said grooves for engagingthe electrode leads of a tube having its tubulation extending throughsaid chamber, mean-s for securing each of said contacts in itsrespective groove including a stud extending through the portion of saidbody between the outer end of the respective groove and the exteriorsurface of said body, a fastener on the outer end of each of said studs,a heating element of annular coil form situated within the centralchamber and dimensioned to surround an exhaust tubulation extendingtherethrough, a removable and replaceable annular heating elementsupport situated between the heating element and the wall of saidchamber, said heating element support having on the interior surfacethereof a plurality of outstanding portions engaging and supporting inspaced relationship from each other the respective turns of said heatingelement, and retaining means for releasably securing said heatingelement support in said chamber.

9. An electronic tube tubulation tip-off oven comprising a one-pieceannular ceramic body having a central chamber through which the exhausttubulation of an electronic tube is adapted to extend, a plurality ofgrooves in one end face of said body extending radially from saidchamber and terminating in spaced relation with the marginal edge ofsaid end face, electrical contacts extending radially in said groovesand adapted to engage the electrode leads of tubes having pin circles ofdifierent diameters, means for securing each of said contacts in itsrespective groove including a stud extending through said body to theexterior surface thereof, a heating element of annular coil formsituated within the central chamber dimensioned to surround an exhausttubulation extending therethrough and connected to a pair of said studs,a removable and replaceable annular heating element support situatedbetween the heating element and the wall of said chamber, said heatingelement support having on the interior surface thereof a plurality ofoutstanding portions engaging and supporting in spaced relationship fromeach other the respective turns of said heating element, and retainingmeans for releasably securing said heating element support in saidchamber.

10. An electronic tubulation tip-off oven comprising an annular ceramicone-piece body having a central axially extending throughbore providinga chamber through which the exhaust tubulation of an electronic tube isadapted to extend, a heating element of coaxial annular coil tor-msituated within said chamber :and dimensioned to coaxially surround anexhaust tubulation extending therethrough, a removable and replaceablecoaxial annular heating element support situated between the heatingelement and the wall of said chamber, said heating element supporthaving on the interior surface thereof a plurality of outstandingportions of continuous annular coil form dimensioned for looselyengaging and support-ing in spaced relation from each other therespective turns of said heating element so as to prevent said turnsfrom sagging into short-circuiting contact with each other, terminalsfor said heating element on the exterior of said body, said body havinggrooves in one end thereof through which end portions of said heatingelement may extend 7 g to said terminals, and retaining means forreleasably 2,278,500 Smith Apr. 7, 1942 securing said heating elementsupport in said chamber and 2,813,182 Van Alen Nov. 12, 1957 coveringsaid gr'oove's. 2,963,529 Sdhmidt Dec. 6, 1960 2,986,846 Clarke et :al.June 6, 196 1 References Cited in the fileof this patent 5 3,002,076Massey S t, 26, 19 1 UNITED STATES PATENTS FOREIGN PATENTS 1,654,314Tuttle Dec. 27, 1927 859,353 France June 3, 194 0

1. AN ELECTRONIC TUBE TUBULATION TIP-OFF OVEN COMPRISING A BODY HAVING ACENTRAL CHAMBER THROUGH WHICH THE EXHAUST TUBULATION OF A TUBE ISADAPTED TO EXTEND, A HEATING ELEMENT OF ANNULAR COIL FORM SITUATEDWITHIN SAID CHAMBER AND DIMENSIONED TO SURROUND AN EXHAUST TUBULATIONEXTENDING THERETHROUGH, A REMOVABLE AND REPLACEABLE HEATING ELEMENTSUPPORT SITUATED BETWEEN THE HEATING ELEMENT AND THE WALL OF SAIDCHAMBER, SAID SUPPORT HAVING ON THE INTERIOR SURFACE THEREOF A PLURALITYOF ELECTRICALLY INSULATIVE OUTSTANDING PORTIONS RESPECTIVELY ENGAGINGAND CONTINUOUSLY SUPPORTING IN NON-SHORT-CIRCUITING RELATIONSHIPRESPECTIVE SUCCESSIVE INCREMENTS OF SAID HEATING ELEMENT, AND RETAININGMEANS AT LEAST PARTIALLY CLOSING THE BOTTOM OF SAID CHAMBER FORRELEASABLY SECURING SAID HEATING ELEMENT SUPPORT IN SAID CHAMBER TOPERMIT SAID SUPPORT, UPON RELEASE, TO FALL FREELY FROM SAID CHAMBER.